﻿using System.Collections.Generic;
using UnityEngine;
using UnityEngine.XR.ARFoundation;

/// <summary>
/// This plane visualizer demonstrates the use of a feathering effect
/// at the edge of the detected plane, which reduces the visual impression
/// of a hard edge.
/// </summary>
[RequireComponent(typeof(ARPlaneMeshVisualizer), typeof(MeshRenderer), typeof(ARPlane))]
public class ARFeatheredPlaneMeshVisualizer : MonoBehaviour
{
	[Tooltip("The width of the texture feathering (in world units).")]
	[SerializeField]
	float m_FeatheringWidth = 0.2f;

	/// <summary>
	/// The width of the texture feathering (in world units).
	/// </summary>
	public float featheringWidth
	{
		get { return m_FeatheringWidth; }
		set { m_FeatheringWidth = value; }
	}

	void Awake()
	{
		m_PlaneMeshVisualizer = GetComponent<ARPlaneMeshVisualizer>();
		m_FeatheredPlaneMaterial = GetComponent<MeshRenderer>().material;
		m_Plane = GetComponent<ARPlane>();
	}

	void OnEnable()
	{
		m_Plane.boundaryChanged += ARPlane_boundaryUpdated;
	}

	void OnDisable()
	{
		m_Plane.boundaryChanged -= ARPlane_boundaryUpdated;
	}

	void ARPlane_boundaryUpdated(ARPlaneBoundaryChangedEventArgs eventArgs)
	{
		GenerateBoundaryUVs(m_PlaneMeshVisualizer.mesh);
	}

	/// <summary>
	/// Generate UV2s to mark the boundary vertices and feathering UV coords.
	/// </summary>
	/// <remarks>
	/// The <c>ARPlaneMeshVisualizer</c> has a <c>meshUpdated</c> event that can be used to modify the generated
	/// mesh. In this case we'll add UV2s to mark the boundary vertices.
	/// This technique avoids having to generate extra vertices for the boundary. It works best when the plane is 
	/// is fairly uniform.
	/// </remarks>
	/// <param name="mesh">The <c>Mesh</c> generated by <c>ARPlaneMeshVisualizer</c></param>
	void GenerateBoundaryUVs(Mesh mesh)
	{
		int vertexCount = mesh.vertexCount;

		// Reuse the list of UVs
		s_FeatheringUVs.Clear();
		if (s_FeatheringUVs.Capacity < vertexCount) { s_FeatheringUVs.Capacity = vertexCount; }

		mesh.GetVertices(s_Vertices);

		Vector3 centerInPlaneSpace = s_Vertices[s_Vertices.Count - 1];
		Vector3 uv = new Vector3(0, 0, 0);
		float shortestUVMapping = float.MaxValue;

		// Assume the last vertex is the center vertex.
		for (int i = 0; i < vertexCount - 1; i++)
		{
			float vertexDist = Vector3.Distance(s_Vertices[i], centerInPlaneSpace);

			// Remap the UV so that a UV of "1" marks the feathering boudary.
			// The ratio of featherBoundaryDistance/edgeDistance is the same as featherUV/edgeUV.
			// Rearrange to get the edge UV.
			float uvMapping = vertexDist / Mathf.Max(vertexDist - featheringWidth, 0.001f);
			uv.x = uvMapping;

			// All the UV mappings will be different. In the shader we need to know the UV value we need to fade out by.
			// Choose the shortest UV to guarentee we fade out before the border.
			// This means the feathering widths will be slightly different, we again rely on a fairly uniform plane.
			if (shortestUVMapping > uvMapping) { shortestUVMapping = uvMapping; }

			s_FeatheringUVs.Add(uv);
		}

		m_FeatheredPlaneMaterial.SetFloat("_ShortestUVMapping", shortestUVMapping);

		// Add the center vertex UV
		uv.Set(0, 0, 0);
		s_FeatheringUVs.Add(uv);

		mesh.SetUVs(1, s_FeatheringUVs);
		mesh.UploadMeshData(false);
	}

	static List<Vector3> s_FeatheringUVs = new List<Vector3>();

	static List<Vector3> s_Vertices = new List<Vector3>();

	ARPlaneMeshVisualizer m_PlaneMeshVisualizer;

	ARPlane m_Plane;

	Material m_FeatheredPlaneMaterial;
}


